Image coding method, image decoding method, image coding apparatus, and image decoding apparatus

Abstract

An image coding method includes: deriving a candidate for a motion vector predictor from a co-located motion vector; adding the candidate to a list; selecting the motion vector predictor from the list; and coding a current block and coding a current motion vector, wherein the deriving includes: deriving the candidate by a first derivation scheme in the case of determining that each of a current reference picture and a co-located reference picture is a long-term reference picture; and deriving the candidate by a second derivation scheme in the case of determining that each of the current reference picture and the co-located reference picture is a short-term reference picture.

The invention claimed is: 
     
       1. A decoding method of decoding each block among blocks of pictures, the decoding method comprising:
 deriving a candidate for a motion vector predictor to be used in decoding of a motion vector for a current block to be decoded, from a first motion vector of a first block included in a first picture, the first picture being different from a picture that includes the current block; 
 adding the derived candidate to a list of candidates; 
 selecting one motion vector predictor from the list of candidates; and 
 decoding the motion vector of the current block using the selected motion vector predictor, and decoding the current block using the motion vector and a reference picture of the current block, 
 wherein the reference picture of the current block is different from the first picture, and 
 wherein the deriving includes: 
 determining whether the reference picture of the current block is a long-term reference picture or a short-term reference picture, and whether a first reference picture of the first block is a long-term reference picture or a short-term reference picture; 
 deriving the candidate from the first motion vector without scaling based on a temporal distance in the case of determining that each of the reference picture of the current block and the first reference picture of the first block is a long-term reference picture; and 
 deriving the candidate from the first motion vector by scaling based on a temporal distance in the case of determining that each of the reference picture of the current block and the first reference picture of the first block is a short-term reference picture. 
 
     
     
       2. A decoding apparatus that decodes each block among blocks of pictures, the decoding apparatus comprising:
 a deriving unit configured to derive a candidate for a motion vector predictor to be used in decoding of a motion vector for a current block to be decoded, from a first motion vector of a first block included in a first picture, the first picture being different from a picture that includes the current block; 
 an adding unit configured to add the derived candidate to a list of candidates; 
 a selecting unit configured to select one motion vector predictor from the list of candidates; and 
 a decoder configured to decode the motion vector of the current block using the selected motion vector predictor, and decode the current block using the motion vector and a reference picture of the current block, 
 wherein the reference picture of the current block is different from the first picture, and 
 wherein the deriving unit is configured to: 
 determine whether the reference picture of the current block is a long-term reference picture or a short-term reference picture, and whether a first reference picture of the first block is a long-term reference picture or a short-term reference picture; 
 derive the candidate from the first motion vector without scaling based on a temporal distance in the case of determining that each of the reference picture of the current block and the first reference picture of the first block is a long-term reference picture; and 
 derive the candidate from the first motion vector by scaling based on a temporal distance in the case of determining that each of the reference picture of the current block and the first reference picture of the first block is a short-term reference picture.